1. Technical Field
The invention relates generally to precision measurement instruments, and particularly to calipers with a movable jaw for measuring the dimensions of an object.
2. Description of the Related Art
Calipers are known that utilize pairs of jaws for determining measurements. A first jaw is generally fixed at one end of a measurement scale while a second jaw is attached to a slider assembly that moves along the measurement scale. An outer dimension of an object may be measured by arranging the object between and against inner surfaces of the first and second jaws. An inner dimension of an object may be measured by arranging outer surfaces of the first and second jaws between and against the inner surfaces of the object (e.g. the walls of a hole). The slider assembly may be moved with a user's thumb, and a thumb wheel may be provided for enabling controlled movement of the slider. One exemplary caliper utilizing a thumb wheel is described in U.S. Pat. No. 7,533,474, which is hereby incorporated herein by reference in its entirety.
For measuring the distance between the jaws of the caliper, electronic position encoders may be used, based on low-power inductive, capacitive, or magnetic position sensing technology. In general, such an encoder may comprise a readhead and a scale. The readhead may generally comprise a readhead sensor and readhead electronics. The readhead outputs signals that vary as a function of the position of the readhead sensor relative to the scale along a measuring axis. The scale may be affixed to an elongated scale member that includes a fixed first measuring jaw. The readhead is affixed to a slider assembly including the second measuring jaw, which is movable along the scale member. Measurements of the distance between the two measuring jaws may be determined based on the signals from the readhead. Exemplary electronic calipers are disclosed in commonly assigned
U.S. Pat. Nos. RE37490, 5,574,381, and 5,973,494, each of which is hereby incorporated by reference in its entirety. A prior art electronic caliper that is capable of measuring force is disclosed in U.S. Patent Publication No. 2003/0047009. As described in the '009 publication, one deficiency in the use of prior calipers is the variation in force which can be applied by the measuring jaws and the differences in measurement which can occur as a result. Particularly when a soft object is being measured, the measurement of the object may be unreliable or non-repeatable because one may apply either a higher force on the jaws of the caliper such that the soft object is “more compressed”, or apply a lower force such that the soft object is “less compressed”. The '009 publication discloses a caliper that is capable of measuring both the size and force applied to an object, which may be analyzed to provide more repeatable measurements. However, the force sensing and indicating features of the caliper of the '009 publication may be considered “overkill” in many applications, and/or may be considered too expensive and/or complex by many caliper users. A need exists for improving measurement force control and/or repeatability in a caliper in an economical, ergonomically convenient, repeatable, and intuitively understandable manner.